Re: [multipathtcp] High-level design decisions /architecture

[William Herrin <[e-mail]>]

On Mon, Nov 2, 2009 at 6:45 PM, marcelo bagnulo braun
<[e-mail]> wrote:
>> I'm concerned about this idea. One of the corner cases where shim6
>> falls apart is: once the connection migrates away from the original
>> addresses, how do the endpoints decide whether a new connection
>> request for the original addresses means the migrated addresses or the
>> current holder of the addresses? Think: FTP.
>>
>
> could you expand on this?
> I wasn't aware shim6 falls apart in any case neither this particular
> approach...

Hi Marcelo,

Consider the following scenario:

Host A comes online with 1.2.3.4.
Host A requests a new TCP connection to 5.6.7.8.
Established with host B at 5.6.7.8.
Host B adds 8.7.6.5
Host B removes 5.6.7.8
Host C comes online with 5.6.7.8.
Host A requests a new TCP connection to 5.6.7.8.

Which host does A connect to?

If the answer is C, protocols like FTP which initiate multiple TCP
connections to the same IP address fail once an endpoint gives up its
original address. That'll also impact web browsers which employ dns
pinning.

If the answer is B, I can hijack hotmail's IPs with respect to your
mail server for the few fractions of a second it takes to establish
and move a TCP connection over to an IP address I legitimately
control. You'll then indefinitely send subsequent hotmail-addressed
email to me. If I diligently pass it on to hotmail, you may never even
know.

If we identify the connection by the original IP address even after
that address is gone, effectively lying to the application, we can
induce it to incorrect behavior. That can have security implications
that may be hard to get a handle on.

Regards,
Bill Herrin

-- 
William D. Herrin ................ [e-mail]  [e-mail]
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